1. Field of the Invention
The present invention relates to a superconducting input interface circuit for a superconducting circuit, and more specifically to a superconducting interface circuit which transform a signal sent by an ordinary electronic circuit to a suitable signal for a superconducting circuit.
2. Description of related art
When a superconducting device or a superconducting integrated circuit is adapted to an electronic equipment, it needs to be associated with a conventional electronic circuit operating at an ordinary temperature, since it is still impossible for the superconducting device or the superconducting integrated circuit to complete the entire electronic equipment.
Owing to the real nature of superconducting phenomena, such as problems of cooling etc., superconducting devices utilized in conventional electronic equipment are limited to a switching device and a sensor device including a Josephson junction, a resistor, a capacitor and an inductor. Therefore, a complicated circuit still can not be composed of only the superconducting devices alone. Moreover, the superconducting circuit has a small voltage swing range less than a few millivolts. By this, a weak signal of a few millivolts or a few microvolts is transferred through the superconducting circuit.
In the prior art, in order to transmit a signal of several volts from an ordinary electronic circuit to the superconducting circuit, the signal should be converted to have a voltage swing of a few millivolts or a few microvolts by a normal conducting interface circuit, and then this small voltage swing signal is sent to the superconducting circuit cooled by liquid nitrogen or liquid helium.
This small voltage swing signal sent to the superconducting circuit from the interface circuit is easily affected and disturbed by external electromagnetic waves. Therefore, multiplexing and coding of the small voltage swing signal are restricted so as to decrease the possibility of introducing an error from such processing. This restriction of the multiplexing and coding of the small voltage swing signal leads to an increase in the number of signal lines. In addition, since the above mentioned superconducting circuit has a small voltage/current gain, it has insufficient drivability. In order to compensate for the drivability of the superconducting circuit, the number of the signal lines further increases.
The stable transmission of the small voltage swing signal also requires a complete electromagnetic shield around the signal lines. The electromagnetic shield needs additional space.
The increase of the number of the signal lines and the attachment of the electromagnetic shield bring difficulties for realizing a highly integrated superconducting circuit.